Glaucoma is the second leading cause for blindness worldwide. Primary angle-closure glaucoma is one of the most common sub-types of glaucoma. Evaluating the anterior chamber angle of the eye is an important component in glaucoma diagnosis and management. Gonioscopy remains the clinical standard for assessing the anterior chamber angle in the eye. However, gonioscopy is a subjective method and can be easily affected by factors including patient cooperation, examiner skill, and the type of lens used. Moreover, gonioscopy does not provide quantitative evaluation of the anterior chamber angle.
Ultrasound biomicroscopy (UBM) is another method for providing high-resolution images of the anterior chamber angle. The disadvantages of UBM include invasive contact with the eye using a coupling medium, anesthesia, need for a skilled examiner, and long image acquisition time. Additionally,
Scheimpflug imaging devices, such as Pentacam (Oculus, Lynnwood, Wash., USA) or Galilei (Ziemer Ophthalmic Systems AG, Switzerland), are non-contact instruments that provide another method for imaging the anterior segment of the eye. However, Scheimpflug imaging does not provide sufficient information of the anterior chamber angle due to light scattering and limited image resolution. Therefore, methods for non-invasive imaging of the anterior chamber angle of the eye that provide quantitative detail and measurement are of substantial clinical importance.
Optical coherence tomography (OCT) is a non-contact imaging modality for high-resolution, depth-resolved cross-sectional, and 3-dimensional (3D) imaging of biological tissue. Among its many applications, ocular imaging in particular has found widespread clinical use. OCT imaging can be performed quickly and easily with minimal expertise. It can provide cross-sectional images of the anterior chamber angle with micron level resolution. These advantages make OCT suitable for both qualitative and quantitative angle evaluation. Several parameters, such as angle opening distance (AOD), trabecular-iris space area (TISA), and angle recess area (ARA), have been developed to provide quantitative assessment of the anterior chamber angle. These parameters had been proven to have excellent correlation with gonioscopy in terms of the identification of occludable angles.
Traditional OCT technique commonly acquires 2-dimensional (2D) images of one angle location at a time. Alternatively, the OCT image may contain two opposite angles (such as temporal and nasal), if wide-scan anterior segment images are acquired. Anterior chamber angle configuration may vary quickly even inside the same angle quadrant. Therefore, the 2D-OCT technique has its limitations and cannot provide complete information of the entire angle quadrant. OCT scan patterns to image the anterior chamber angle 3-dimensionally (3D) and methods that provide for qualitative and quantitative 3D angle assessment would enable OCT to become a clinically important non-invasive glaucoma diagnosis and management technique for 3D imaging and measuring of the anterior chamber angle of the eye.